The present invention concerns a method of regulating an internal combustion engine, in particular with a lean-bum mode of operation, to achieve predeterminable nitrogen oxide emission values for the internal combustion engine, and a corresponding regulating apparatus and internal combustion engine.
It is already known from EP 0 259 382 B1 for an internal combustion engine for driving an electrical generator to be operated with constant nitrogen oxide emission values, by regulating the mixture pressure upstream of the inlet valves of the cylinders in dependence on the electrical power delivered by the generator. In that situation the reference value in respect of the mixture pressure upstream of the inlet valves is taken from a family of curves which shows the dependency of the mixture pressure on the delivered electrical power, at constant emission values. Then, the measured actual value of the pressure upstream of the inlet valves is regulated to its reference value determined by way of the family of curves, by way of adjustment of the fuel-air ratio in a gas mixer. The curve used for that purpose is produced by measuring at least two operating points involving identical NOx emission values. By means of that previously known method, it is possible for an internal combustion engine to very accurately maintain the desired emission values in a wide power range. The system known from the stated European patent enjoys the advantage that it involves practically no wear and ageing of sensitive sensors.
European patent application EP 1 225 330 A2 sets forth a further improved system of the general kind set forth, in which the regulating layout known from EP 0 259 382 B1 has been further supplemented by ignition timing adjustment in order to provide a regulating reserve margin for rapid reaction to changes in load, in any operating condition. In addition that regulating system serves to always operate the internal combustion engine at optimum efficiency.
A disadvantage of those known regulating systems is that the pressure upstream of the inlet valves of the cylinders must necessarily be available.